Re: Phosphates affect on aquatic plants?

Hi Stephanie-

That's a pretty big area you're interested in! Any book you can find on limnology will be able to tell you about phosphate and plants- it's a very widely studied area by aquatic biologists and chemists. If you can find it, I'd suggest Robert G. Wetzel's text, which is entitled, strangely enough, "Limnology" (it's published by Saunders (Philadelphia), and I believe it's in its 3rd edition, though there are also 1st (1974) and 2nd (1983) editions available).

In any case, phosphate is generally the limiting nutrient for freshwater plants. Things are a little different in the ocean, where nitrogen is generally limiting, so I'll assume you're talking fresh water here.

Both macrophytes (the big aquatic plants you can see in lakes and ponds), and phytoplankton are limited by phosphate, and so their growth is affected by how much phosphate gets to them. In phytoplankton, that generally is from phosphate that is mixed up from deep water by the wind- that's pretty difficult to measure, so I wouldn't recommend it for a project. Macrophytes, on the other hand, get most of their phosphate from the sediments they live in (here's a discussion group posting about that, and a review of how water moves around in aquatic plants by Ole Pedersen you can check out).

So, I'd suggest that any project you'd want to do would be with macrophytes- measuring phosphate levels isn't too tricky, you can get kits for that at any aquarium store (here's an example of one of those kits). So what you could do is try something like measuring phosphate levels in the sediments around different types of plants, and comparing that with sediments in places where there are no plants. You could also try something like measuring the phosphate inside the plants (by grinding them up in a blender, or crushing them with a mortar and pestle- your teacher should be able to help you there), and compare that with the phosphate in the sediments around them, and the phosphate in the water around them.

Good Luck!

Rob Campbell, MAD Scientist